http://gcc.gnu.org/bugzilla/show_bug.cgi?id=55319
Bug #: 55319 Summary: Using -fwhole-program inhibits optimization Classification: Unclassified Product: gcc Version: 4.7.2 Status: UNCONFIRMED Severity: normal Priority: P3 Component: c++ AssignedTo: unassig...@gcc.gnu.org ReportedBy: m1010...@gmail.com Created attachment 28681 --> http://gcc.gnu.org/bugzilla/attachment.cgi?id=28681 The preprocessed source The attached code is a template-based brainfuck interpreter, and the brainfuck code in it prints "Hello world!". When the attached code is compiled with "g++ -std=c++11 -O2 bf.ii", it produces a series of calls to _IO_putc which directly print "Hello World!". However, when compiled with "g++ -std=c++11 -O2 -fwhole-program bf.ii", it produces a more direct and less optimized interpretation of the associated brainfuck. $ gcc -v Using built-in specs. COLLECT_GCC=gcc COLLECT_LTO_WRAPPER=/usr/lib/gcc/x86_64-unknown-linux-gnu/4.7.2/lto-wrapper Target: x86_64-unknown-linux-gnu Configured with: /build/src/gcc-4.7.2/configure --prefix=/usr --libdir=/usr/lib --libexecdir=/usr/lib --mandir=/usr/share/man --infodir=/usr/share/info --with-bugurl=https://bugs.archlinux.org/ --enable-languages=c,c++,ada,fortran,go,lto,objc,obj-c++ --enable-shared --enable-threads=posix --with-system-zlib --enable-__cxa_atexit --disable-libunwind-exceptions --enable-clocale=gnu --disable-libstdcxx-pch --enable-libstdcxx-time --enable-gnu-unique-object --enable-linker-build-id --with-ppl --enable-cloog-backend=isl --disable-ppl-version-check --disable-cloog-version-check --enable-lto --enable-gold --enable-ld=default --enable-plugin --with-plugin-ld=ld.gold --with-linker-hash-style=gnu --enable-multilib --disable-libssp --disable-build-with-cxx --disable-build-poststage1-with-cxx --enable-checking=release Thread model: posix gcc version 4.7.2 (GCC)